Global namespace for a hierarchical set of file systems

ABSTRACT

One embodiment provides a method for storage management in a hierarchical file system. The method includes tracking directories for sub-file systems of the hierarchical file system. A request for a unique directory in the hierarchical file system is received. The sub-file system of the hierarchical file system containing the unique directory is provided while ensuring that each directory resides in only one sub-file system. The system also maintains, in a top-file system, a corresponding directory and a symbolic pointer which points from the corresponding directory to a sub-file system where a given directory resides. Creation of new directories in sub-file systems also includes creation of corresponding directories in the top-file system and symbolic pointers from corresponding directory to new directory.

BACKGROUND

With storage requirements growing, information technology (IT)departments are expected to maintain and provide for storage in thescale of petabytes. However, as filesystems systems grow, theprobability of failures/corruptions, either due to software bugs orhardware failure, increases. Recovery from failures takes longer andlonger as more and more data and metadata need to be scanned to verifyintegrity and correct inconsistencies. Ultimately filesystemavailability and robustness degrades.

SUMMARY

Embodiments relate to storage management in hierarchical file systems.One embodiment provides a method for storage management in ahierarchical file system. The method includes tracking directories forsub-file systems of the hierarchical file system. A request for a uniquedirectory in the hierarchical file system is received. The sub-filesystem of the hierarchical file system containing the unique directoryis provided while ensuring that each directory resides in only onesub-file system. The system also maintains, in a top-file system, acorresponding directory and a symbolic pointer which points from thecorresponding directory to a sub-file system where a given directoryresides. Creation of new directories in sub-file systems also includescreation of corresponding directories in the top-file system andsymbolic pointers from corresponding directory to new directory.

These and other features, aspects and advantages of the presentinvention will become understood with reference to the followingdescription, appended claims and accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a cloud computing environment, according to anembodiment;

FIG. 2 depicts a set of abstraction model layers, according to anembodiment;

FIG. 3 is a network architecture for storage management providing uniqueinode numbers across multiple file system namespaces, according to anembodiment;

FIG. 4 shows a representative hardware environment that may beassociated with the servers and/or clients of FIG. 1, according to anembodiment;

FIG. 5 is a block diagram illustrating processors for storage managementproviding unique inode numbers across multiple file system namespaces,according to an embodiment;

FIG. 6 illustrates a high-level file system structure, according to anembodiment;

FIG. 7 is a block diagram illustrating an example of a file systemincluding a top-file system portion and sub-file systems, according toan embodiment; and

FIG. 8 illustrates a block diagram for a process for storage managementin a hierarchical file system, according to one embodiment.

DETAILED DESCRIPTION

The descriptions of the various embodiments have been presented forpurposes of illustration, but are not intended to be exhaustive orlimited to the embodiments disclosed. Many modifications and variationswill be apparent to those of ordinary skill in the art without departingfrom the scope and spirit of the described embodiments. The terminologyused herein was chosen to best explain the principles of theembodiments, the practical application or technical improvement overtechnologies found in the marketplace, or to enable others of ordinaryskill in the art to understand the embodiments disclosed herein.

It is understood in advance that although this disclosure includes adetailed description of cloud computing, implementation of the teachingsrecited herein are not limited to a cloud computing environment. Rather,embodiments of the present invention are capable of being implemented inconjunction with any other type of computing environment now known orlater developed.

One or more embodiments provide for retrospective snapshot creation. Oneembodiment includes creating, by a processor, a first snapshot thatcaptures logical state of a data store at a first key. Creation of thefirst snapshot is based on determining a log offset corresponding to thefirst key, determining existence of a second snapshot that captureslogical state of the data store and recording a retrospective snapshotat a last valid log address offset prior to the first key upon adetermination that the second snapshot exists based on determining atleast one of: whether log address offsets from a first log entry of alog to a log entry of the log at the first key are contiguous andwhether log address offsets from the second snapshot to the first keyare contiguous.

Cloud computing is a model of service delivery for enabling convenient,on-demand network access to a shared pool of configurable computingresources (e.g., networks, network bandwidth, servers, processing,memory, storage, applications, virtual machines (VMs), and services)that can be rapidly provisioned and released with minimal managementeffort or interaction with a provider of the service. This cloud modelmay include at least five characteristics, at least three servicemodels, and at least four deployment models.

Characteristics are as Follows:

On-demand self-service: a cloud consumer can unilaterally provisioncomputing capabilities, such as server time and network storage, asneeded and automatically, without requiring human interaction with theservice's provider.

Broad network access: capabilities are available over a network andaccessed through standard mechanisms that promote use by heterogeneous,thin or thick client platforms (e.g., mobile phones, laptops, and PDAs).

Resource pooling: the provider's computing resources are pooled to servemultiple consumers using a multi-tenant model, with different physicaland virtual resources dynamically assigned and reassigned according todemand. There is a sense of location independence in that the consumergenerally has no control or knowledge over the exact location of theprovided resources but may be able to specify location at a higher levelof abstraction (e.g., country, state, or data center).

Rapid elasticity: capabilities can be rapidly and elasticallyprovisioned and, in some cases, automatically, to quickly scale out andrapidly released to quickly scale in. To the consumer, the capabilitiesavailable for provisioning often appear to be unlimited and can bepurchased in any quantity at any time.

Measured service: cloud systems automatically control and optimizeresource use by leveraging a metering capability at some level ofabstraction appropriate to the type of service (e.g., storage,processing, bandwidth, and active consumer accounts). Resource usage canbe monitored, controlled, and reported, thereby providing transparencyfor both the provider and consumer of the utilized service.

Service Models are as Follows:

Software as a Service (SaaS): the capability provided to the consumer isthe ability to use the provider's applications running on a cloudinfrastructure. The applications are accessible from various clientdevices through a thin client interface, such as a web browser (e.g.,web-based email). The consumer does not manage or control the underlyingcloud infrastructure including network, servers, operating systems,storage, or even individual application capabilities, with the possibleexception of limited consumer-specific application configurationsettings.

Platform as a Service (PaaS): the capability provided to the consumer isthe ability to deploy onto the cloud infrastructure consumer-created oracquired applications created using programming languages and toolssupported by the provider. The consumer does not manage or control theunderlying cloud infrastructure including networks, servers, operatingsystems, or storage, but has control over the deployed applications andpossibly application-hosting environment configurations.

Infrastructure as a Service (IaaS): the capability provided to theconsumer is the ability to provision processing, storage, networks, andother fundamental computing resources where the consumer is able todeploy and run arbitrary software, which can include operating systemsand applications. The consumer does not manage or control the underlyingcloud infrastructure but has control over operating systems, storage,deployed applications, and possibly limited control of select networkingcomponents (e.g., host firewalls).

Deployment Models are as Follows:

Private cloud: the cloud infrastructure is operated solely for anorganization. It may be managed by the organization or a third party andmay exist on-premises or off-premises.

Community cloud: the cloud infrastructure is shared by severalorganizations and supports a specific community that has shared concerns(e.g., mission, security requirements, policy, and complianceconsiderations). It may be managed by the organizations or a third partyand may exist on-premises or off-premises.

Public cloud: the cloud infrastructure is made available to the generalpublic or a large industry group and is owned by an organization sellingcloud services.

Hybrid cloud: the cloud infrastructure is a composition of two or moreclouds (private, community, or public) that remain unique entities butare bound together by standardized or proprietary technology thatenables data and application portability (e.g., cloud bursting for loadbalancing between clouds).

A cloud computing environment is a service oriented with a focus onstatelessness, low coupling, modularity, and semantic interoperability.At the heart of cloud computing is an infrastructure comprising anetwork of interconnected nodes.

Referring now to FIG. 1, an illustrative cloud computing environment 50is depicted. As shown, cloud computing environment 50 comprises one ormore cloud computing nodes 10 with which local computing devices used bycloud consumers, such as, for example, personal digital assistant (PDA)or cellular telephone 54A, desktop computer 54B, laptop computer 54C,and/or automobile computer system 54N may communicate. Nodes 10 maycommunicate with one another. They may be grouped (not shown) physicallyor virtually, in one or more networks, such as private, community,public, or hybrid clouds as described hereinabove, or a combinationthereof. This allows the cloud computing environment 50 to offerinfrastructure, platforms, and/or software as services for which a cloudconsumer does not need to maintain resources on a local computingdevice. It is understood that the types of computing devices 54A-N shownin FIG. 1 are intended to be illustrative only and that computing nodes10 and cloud computing environment 50 can communicate with any type ofcomputerized device over any type of network and/or network addressableconnection (e.g., using a web browser).

Referring now to FIG. 2, a set of functional abstraction layers providedby the cloud computing environment 50 (FIG. 1) is shown. It should beunderstood in advance that the components, layers, and functions shownin FIG. 2 are intended to be illustrative only and embodiments of theinvention are not limited thereto. As depicted, the following layers andcorresponding functions are provided:

Hardware and software layer 60 includes hardware and softwarecomponents. Examples of hardware components include: mainframes 61; RISC(Reduced Instruction Set Computer) architecture based servers 62;servers 63; blade servers 64; storage devices 65; and networks andnetworking components 66. In some embodiments, software componentsinclude network application server software 67 and database software 68.

Virtualization layer 70 provides an abstraction layer from which thefollowing examples of virtual entities may be provided: virtual servers71; virtual storage 72; virtual networks 73, including virtual privatenetworks; virtual applications and operating systems 74; and virtualclients 75.

In one example, a management layer 80 may provide the functionsdescribed below. Resource provisioning 81 provides dynamic procurementof computing resources and other resources that are utilized to performtasks within the cloud computing environment. Metering and pricing 82provide cost tracking as resources are utilized within the cloudcomputing environment and billing or invoicing for consumption of theseresources. In one example, these resources may comprise applicationsoftware licenses. Security provides identity verification for cloudconsumers and tasks as well as protection for data and other resources.User portal 83 provides access to the cloud computing environment forconsumers and system administrators. Service level management 84provides cloud computing resource allocation and management such thatrequired service levels are met. Service Level Agreement (SLA) planningand fulfillment 85 provide pre-arrangement for, and procurement of,cloud computing resources for which a future requirement is anticipatedin accordance with an SLA.

Workloads layer 90 provides examples of functionality for which thecloud computing environment may be utilized. Examples of workloads andfunctions which may be provided from this layer include: mapping andnavigation 91; software development and lifecycle management 92; virtualclassroom education delivery 93; data analytics processing 94; andtransaction processing 95. As mentioned above, all of the foregoingexamples described with respect to FIG. 2 are illustrative only, and theinvention is not limited to these examples.

It is understood all functions of one or more embodiments as describedherein may be typically performed by the processing system 300 (FIG. 3)or the autonomous cloud environment 410 (FIG. 4), which can be tangiblyembodied as hardware processors and with modules of program code.However, this need not be the case for non-real-time processing. Rather,for non-real-time processing the functionality recited herein could becarried out/implemented and/or enabled by any of the layers 60, 70, 80and 90 shown in FIG. 2.

It is reiterated that although this disclosure includes a detaileddescription on cloud computing, implementation of the teachings recitedherein are not limited to a cloud computing environment. Rather, theembodiments of the present invention may be implemented with any type ofclustered computing environment now known or later developed.

FIG. 3 illustrates a network architecture 300, in accordance with oneembodiment. As shown in FIG. 3, a plurality of remote networks 302 areprovided, including a first remote network 304 and a second remotenetwork 306. A gateway 301 may be coupled between the remote networks302 and a proximate network 308. In the context of the present networkarchitecture 300, the networks 304, 306 may each take any formincluding, but not limited to, a LAN, a WAN, such as the Internet,public switched telephone network (PSTN), internal telephone network,etc.

In use, the gateway 301 serves as an entrance point from the remotenetworks 302 to the proximate network 308. As such, the gateway 301 mayfunction as a router, which is capable of directing a given packet ofdata that arrives at the gateway 301, and a switch, which furnishes theactual path in and out of the gateway 301 for a given packet.

Further included is at least one data server 314 coupled to theproximate network 308, which is accessible from the remote networks 302via the gateway 301. It should be noted that the data server(s) 314 mayinclude any type of computing device/groupware. Coupled to each dataserver 314 is a plurality of user devices 316. Such user devices 316 mayinclude a desktop computer, laptop computer, handheld computer, printer,and/or any other type of logic-containing device. It should be notedthat a user device 311 may also be directly coupled to any of thenetworks in some embodiments.

A peripheral 320 or series of peripherals 320, e.g., facsimile machines,printers, scanners, hard disk drives, networked and/or local storageunits or systems, etc., may be coupled to one or more of the networks304, 306, 308. It should be noted that databases and/or additionalcomponents may be utilized with, or integrated into, any type of networkelement coupled to the networks 304, 306, 308. In the context of thepresent description, a network element may refer to any component of anetwork.

According to some approaches, methods and systems described herein maybe implemented with and/or on virtual systems and/or systems, whichemulate one or more other systems, such as a UNIX system that emulatesan IBM z/OS environment, a UNIX system that virtually hosts a MICROSOFTWINDOWS environment, a MICROSOFT WINDOWS system that emulates an IBMz/OS environment, etc. This virtualization and/or emulation may beimplemented through the use of VMWARE software in some embodiments.

FIG. 4 shows a representative hardware system 400 environment associatedwith a user device 316 and/or server 314 of FIG. 3, in accordance withone embodiment. In one example, a hardware configuration includes aworkstation having a central processing unit 410, such as amicroprocessor, and a number of other units interconnected via a systembus 412. The workstation shown in FIG. 4 may include a Random AccessMemory (RAM) 414, Read Only Memory (ROM) 416, an I/O adapter 418 forconnecting peripheral devices, such as disk storage units 420 to the bus412, a user interface adapter 422 for connecting a keyboard 424, a mouse426, a speaker 428, a microphone 432, and/or other user interfacedevices, such as a touch screen, a digital camera (not shown), etc., tothe bus 412, communication adapter 434 for connecting the workstation toa communication network 435 (e.g., a data processing network) and adisplay adapter 436 for connecting the bus 412 to a display device 438.

In one example, the workstation may have resident thereon an operatingsystem, such as the MICROSOFT WINDOWS Operating System (OS), a MAC OS, aUNIX OS, etc. In one embodiment, the system 400 employs a POSIX® basedfile system. It will be appreciated that other examples may also beimplemented on platforms and operating systems other than thosementioned. Such other examples may include operating systems writtenusing JAVA, XML, C, and/or C++ language, or other programming languages,along with an object oriented programming methodology. Object orientedprogramming (OOP), which has become increasingly used to develop complexapplications, may also be used.

An inode may be referred to as a data structure, which may be used torepresent a file system object. A file system object may be, forexample, a file, a directory, etc. Each inode stores attributes and diskblock location(s) for the file system object's data. Integrity checkssuch as file system consistency check (fsck) have been parallelizedusing techniques, such as inode space division and node delegation tospeed up recovery. However, the time taken to recover/check file systemsis still proportional to the volume of data that needs to be scanned. Tosolve for that, union mount file systems may be used. Instead of asingle file system, multiple smaller file systems or sub-file systems(also referred to as subFSs) are commissioned such that together theyprovide for the cumulative storage needs. Since each sub-file system(also referred to as subFS) is smaller than the whole file system, ifthere is a failure in a sub-file system, recovery is faster. Eachsub-file system is a federated entity, therefore, a failure in onesub-file system does not affect the other sister sub-file systems. Thisimproves availability.

As storage requirements grow, new sub-file systems can be provisioned todistribute the load without degrading recovery time. One key problemwith presenting multiple file systems as a single namespace is that eachindividual file system uses the same set of possible inode numbers. Thiscan cause issues in several different ways. First, applications usingthe namespace expect that different files will have different inodenumbers (this is in fact a core part of the POSIX standard). If twofiles have the same inode number, many applications could fail. Further,file and directory placement at creation time can be devised to ensureeven distribution across all sub-file systems. However, as files growover time, it is possible for one or some sub-file systems under theunion mount point to become too large, increasing recovery time forthose sub-file systems in the event of a failure.

Redistribution of data across sub-file systems is required to ensure noone file system grows too large such that it would have a long recoverytime if it failed and would handle a disproportionate amount of theincoming I/O load. Therefore, data is moved, along with its inode andnamespace, to another sub-file system to rebalance sub-file system size.If inode numbers across sub-file systems weren't unique, such datamovement would cause inode collisions in the target sub-file system.Inode number collisions would complicate the machinery which rebalancesthe spread of data across sub-file systems. One or more embodimentsprovide a solution that maintains unique inode numbers across allsub-file systems.

FIG. 5 is a block diagram illustrating processors for storage managementproviding unique inode numbers across multiple file system namespaces,according to an embodiment. Node 500 includes an inode manager processor510, memory 520 and an inode balancing manager processor 530. The memory520 may be implemented to store instructions and data, where theinstructions are executed by the inode manager processor 510 and theinode balancing manager processor 530. In one example, the inode managerprocessor 510 provides creation of a globally unique inode space acrossall sub-file systems (e.g., sub-file system 625, FIG. 6). The inodemanager processor 510 further provides allocation of a unique range ofinodes to every sub-file system. Together these inodes encompass thesubtree of the file system. In one or more embodiments, an inode numberis unique across all sub-file systems. Therefore, inodes within a cellare unique across all sub-file systems. A cell is an autonomous unitconsisting of logical (inodes, hierarchy) and physical (storage pools,allocation table/inode map) constructs.

In one embodiment, the inode balancing manager processor 530 providesbalancing and re-balancing processing. In one example, starting with thelargest sub-file system by number of inodes or aggregate size, the inodebalancing manager processor 530 performs a greedy algorithm to findcells within it. The inode balancing manager processor 530 furtherquiesces input/output (I/O) operations to every element of the chosencell, and copies the independent file set's inode table to a destinationsub-file system. The inode balancing manager processor 530 notifies afile system allocation manager of a destination sub-file system of thenew storage pools that it is required to manage going forward. The inodebalancing manager processor 530 further updates any pointers/links in atop-file system (also referred to as a TopFS) to a new location of thecell, un-quiesces I/O to a cell, and performs copy-less creation anddeletion of sub-file systems.

In one embodiment, the inode manager processor 510 and the inodebalancing manager processor 530 perform processing such that eachsub-file system consumes a flexible range of inode numbers from a globalinode number pool, therefore ensuring unique inode numbers across allsub-file systems. The inode manager processor acts as a global inodenumber manager to ensure that each sub-file system has enough inodenumbers and that no two sub-file systems have overlapping inode numbers(which would lead to possible data corruption). The top-file system partof the file system (e.g., the portion that binds the sub-file systemstogether) or the individual sub-file systems send requests to the inodemanager processor 510 to request inode numbers (or a range of inodes) touse. The inode manager processor 510 then returns a range of inodenumbers. If a sub-file system needs more inode numbers and none areavailable, the inode manager processor 510 may revoke inode numbers froma sub-file system that doesn't need them and hand them to one that needsit.

In one embodiment, the size of the range of inode numbers is typicallylimited to the range of inodes that may be described by an unsigned 64bit binary number. The number of inode numbers provided to each sub-filesystem is totally under the control of the inode manager processor 510(although sub-file systems may be able to provide hints to the numberthat they are requesting). Limiting the number of inode numbers meansthat sub-file systems will need to send more requests to the inodemanager processor 510 (possibly slowing the system down), whereasincreasing the number of inode numbers means that a sub-file systemcould be assigned too many and need to have them revoked (also possiblyslowing down the system). In one embodiment, the inode manager processor510 starts by issuing smaller inode number ranges to each sub-filesystem. The inode manager processor can then track the sub-file systemsto see how often each sub-file system is requesting additional inodenumbers, and if the request rate passes a predetermined threshold (e.g.,a number of requests per minute, hour, day, etc.), then issue thesub-file system increasingly more inodes in each request to thatsub-file system.

In one embodiment, the inode manager processor 510 tracks the inodenumber ranges assigned to each sub-file system and may be queried by theTopFS (e.g., TopFS 710, FIG. 7) or other daemons in the file system.Each sub-file system may optionally send the inode manager processor 510an update of the number of used inode numbers. In one example, if asub-file system requests a range of inode numbers from the inode managerprocessor 510, but there are no remaining numbers, then the inodemanager processor 510 must revoke inode numbers from one of the sub-filesystems. If the inode manager processor 510 determines how many inodesare used in each sub-file system (from the sub-file systems sendingupdates), then the inode manager processor 510 attempts to revoke aportion of the unused inodes from the sub-file system that has the mostunused inode numbers. If the inode manager processor 510 does notdetermine how many of the inode number ranges each of the sub-filesystems has used, then it must query all of them to make thedetermination (this may be performed in parallel). There are severaltechniques that may be used to revoke an inode number range from one ormore sub-file systems (e.g., at small sample size from each one, a largesample size from one sub-file system, etc.). In one example, eachsub-file system may wait until it runs out of inode numbers beforerequesting more. In another example, the sub-file systems request moreinodes when the number of their unused inodes drops below a threshold(e.g., 40%, 50%, etc.). In one embodiment, each sub-file system musttrack the inode numbers that have been assigned to it and the numbersthat are currently used by executing applications.

In one embodiment, the TopFS may query the inode manager processor 510to learn which sub-file system has consumed how many inodes. Inparticular, if a sub-file system has too many used inodes (e.g., aparticular proportion of unused as compared to used inodes), then thefiles and directories from that sub-file system may be migrated by theinode balancing processor 530 to another sub-file system or a portion ofits data (along with the name space and inode space) may be moved toanother sub-file system without having to handle inode collisions.

FIG. 6 illustrates a high-level file system structure 600, according toan embodiment. In one embodiment, the file system structure 600 is aunion mounted or aggregated file system having a TopFS 610 where a userviews a single namespace. The file system abstraction 620 includes thesub-file systems 625 (e.g., subFS1, subFS2, subFS3, etc.) includingfiles 630 and possibly directories, which are mapped across failuredomains (sub-file systems 625) based upon policy. The storageabstraction 640 includes failure domains (sub-file systems mapped acrossstorage building blocks and include elastic system servers (ESS) 645 andstorage devices 650 (e.g., drives, discs, RAIDs, etc.). In oneembodiment, a sub-file system in a first environment may be configuredas a top-file system in a second environment wherein it maintains adirectory structure of sub-file systems under its control.

In one embodiment, the TopFS 610 maintains the hierarchical directorystructure and does not house data. The sub-file systems 625 have a twolevel namespace of directories and its files. The namespace in the TopFS610 and pointers to sub-file systems 625 include the name of a directoryin a sub-file system 625 that is its inode number in the TopFS 610. Whena user looks up a directory, the system follows the pointer from theTopFS 610 directory to the sub-file system 625, and then finds and readsthe directory with the name of its inode number.

In one embodiment, a policy-based directory creation in the file systemstructure 600 provides a capacity policy with no failure isolation wheredirectories are allocated across all sub-file systems 625 using a roundrobin technique, a technique based on available space, etc. In oneembodiment, the file system structure 600 provides a dataset affinitypolicy with a per-dataset failure isolation that places an entiredataset in a single sub-file system 625, limits datasets to the size ofa sub-file system 625, and where failure will not impact some projectsbut will impact others.

In one or more embodiments, the file system structure 600 provides faulttolerance where datasets in a single failure domain (e.g., a SubFS) cansurvive a failure of any other domain, the TopFS 610 is relatively smalland can recovery quickly, users are provided the option to choosebetween capacity and availability by spreading a single dataset acrossall failure domains, which increases capacity while decreasingavailability, and a single dataset is isolated within a single failuredomain for increasing availability while reducing capacity.

The file system structure 600 provides fault tolerance for softwarewhere each sub-file system 625 can fail and recover independentlywithout impacting other sub-file systems 625, and for hardware whereeach sub-file system 625 is mapped to storage building blocks accordingto performance, capacity, and availability requirements.

In one embodiment, the file system structure 600 provides performancebenefits by parallelizing operations by issuing operations on any numberof sub-file systems 625 simultaneously, depending on configured sub-filesystems 625, where performance may be independent of the number ofsub-file systems 625 (a sub-file system 625 may span all disks). Singlesub-file system 625 improvements help the entire file system structure600, and there are no performance losses for most operations.

In one embodiment, the file system structure 600 provides a capacitybenefit where sub-file system 625 metadata managed separately, allowingmetadata to scale with the number of sub-file systems 625, sub-filesystems 625 are large enough to support most datasets (e.g., 1 to 10 PBin capacity), and to find files, the file system structure 600 onlyneeds to scan an individual failure domain instead of the entire system.

One or more embodiments provide for the TopFS 610 storing a directoryhierarchy, with each directory pointing to a sub-file system 625 for itsdirectory contents. Upon directory creation, the directory is created inthe TopFS 610, and then a directory (named with the inode number of thedirectory in the TopFS 610) is created in a sub-file system 625, and asymbolic pointer from the directory in the TopFS 610 points to thesub-file system 625. The sub-file system 625 in which the directory iscreated is chosen according to a policy. Each directory is stored at theroot of the sub-file system 625 (flat namespace). Each directory in thesub-file system 625 is named using the inode number of the directorythat points to it. Upon access of a directory in the TopFS 610, the filesystem structure 600 follows the pointer to the sub-file system, thenaccess the information stored in the directory with its inode number.Upon access of a file in a directory, the TopFS 610 passes the requeststo the file 630 in the sub-file system 625. In one embodiment,subsequent accesses to the file in the directory do not utilize theTopFS 610 an instead go directory to the file in the given sub-filesystem 625 previously accessed.

FIG. 7 is a block diagram illustrating an example of a file systemincluding the TopFS 710 portion and sub-file systems 725 withdirectories 730, according to an embodiment. In this example, it isshown how the directories Science, Astronomy, Biology and Moon may bestructured in the system.

FIG. 8 illustrates a block diagram for a process 800 for storagemanagement in a hierarchical file system (e.g., file system structure600, or system shown in FIG. 7), according to one embodiment. In block802 process 800 includes tracking directories for sub-file systems(e.g., sub-file systems 625, FIG. 6, 725, FIG. 7) of the hierarchicalfile system. In one embodiment, tracking comprises maintaining a set ofcorresponding directories in the top-file system (710, FIG. 7), eachdirectory corresponding to a unique directory among the sub-file systems(625, FIG. 6, 725, FIG. 7). In one embodiment, tracking furthercomprises maintaining in each of the corresponding directories in thetop-file system, a symbolic pointer which points from the correspondingdirectory to the given sub-file system where the tracked directoryresides. With respect to FIG. 7, the TopFS 710 maintains a correspondingdirectory for Moon which comprises a symbolic pointer to SubFS1 725because the Moon directory resides within SubFS1.

In block 804 a request for a unique directory in the hierarchical filesystem is received. In block 806 the sub-file system containing therequested directory is provided while providing that each directoryresides in one sub-file system.

In one embodiment, process 800 may need to create a new directory and indoing so, must determine that a particular sub-file system in thehierarchal file system has available space for an additional directory.In one embodiment, block 808 compares the available space for eachsub-file system in the hierarchical file system and selects a sub-filesystem with the largest available space. In one embodiment, block 808selects in a round-robin fashion a sub-file system having availablespace for an additional directory. In one embodiment, block 808estimates the size of the additional directory. Estimation could beperformed by analyzing the size of the current directories in thehierarchical file system, analyzing the historical size of directoriesin the hierarchical file system, etc. After estimation is complete,block 808 selects a sub-file system having available space at least aslarge as the estimated size for the additional directory. In oneembodiment, block 808 selects in a round-robin fashion one of thesub-file systems that have sufficient additional space for the estimatedsize of the additional directory. In this configuration, thehierarchical file system is created based on available capacity amongthe sub-file systems.

In one embodiment, block 808 maintains dataset affinity. For new parentdirectories (directors from which no prior created directory relates,e.g., Science in FIG. 7), block 808 operates by determining the sub-filesystem has the requisite available space for the new directory. Forchild directories (e.g., Astronomy, Biology and Moon in FIG. 7), newdirectories are created in the sub-file system of its parent directory(e.g., Science, FIG. 7). In this configuration, the hierarchical filesystem maintains per-dataset fault isolation; failure of other sub-filesystems will not affect availability of an entire dataset on anon-faulting sub-file system, however the entire dataset size is limitedby the size of the sub-file system.

In one embodiment, process 800 further provides block 810 creating theadditional directory in the particular sub-file system. In oneembodiment, creation of the directory in the sub-file system comprisescreating a corresponding directory in the top-file system. Further,block 810 creates a symbolic pointer, in the corresponding directory inthe top-file system, said symbolic pointer pointing to the createdadditional directory in the particular sub-file system.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module” or “system.”Furthermore, aspects of the present invention may take the form of acomputer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for aspects of thepresent invention may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of the present invention are described below with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

References in the claims to an element in the singular is not intendedto mean “one and only” unless explicitly so stated, but rather “one ormore.” All structural and functional equivalents to the elements of theabove-described exemplary embodiment that are currently known or latercome to be known to those of ordinary skill in the art are intended tobe encompassed by the present claims. No claim element herein is to beconstrued under the provisions of 35 U.S.C. section 112, sixthparagraph, unless the element is expressly recited using the phrase“means for” or “step for.”

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. A method for storage management in a hierarchicalset of file system, the method comprising: creating a structure for thehierarchical file system including a top-file system and sub-filesystems that each include files and directories; tracking directoriesfor the sub-file systems of the hierarchical file system; receiving arequest for creation of a unique directory in the hierarchical filesystem; creating, based on applying a directory creation policy, asub-file system of the hierarchical file system containing the uniquedirectory while providing that each directory for the sub-file systemresides in only one sub-file system; and upon a request by a particularsub-file system for more inodes without any inodes available, revokinginode numbers from at least one other sub-file system having unusedinodes; wherein failure in one sub-file system has no affect on othersub-file systems in the hierarchical file system, and each directory inthe sub-file systems is named using an inode number of a directory inthe top file system.
 2. The method of claim 1, wherein trackingcomprises: for each directory in a sub-file system: maintaining acorresponding directory in the top-file system; and maintaining asymbolic pointer in the corresponding directory which points from thecorresponding directory to the sub-file system where the trackeddirectory resides.
 3. The method of claim 1, wherein applying thedirectory creation policy comprises: determining that a particularsub-file system has available space for an additional directory.
 4. Themethod of claim 3, wherein determining comprises: comparing availablespace for each sub-file system; and selecting a sub-file system with thelargest available space.
 5. The method of claim 3, wherein determiningcomprises: estimating a size requirement for the additional directory;and selecting a sub-file system having available space at least as largeas the estimated size requirement for the additional directory.
 6. Themethod of claim 3, wherein determining comprises: selecting, in around-robin fashion, a sub-file system having available space for theadditional directory.
 7. The method of claim 3, wherein determiningcomprises: estimating a size requirement for the additional directory;and selecting, in a round-robin fashion, a sub-file system havingavailable space at least as large as the estimated size requirement forthe additional directory.
 8. The method of claim 3, further comprising:creating a corresponding directory in the top-file system; and creatinga symbolic pointer in the corresponding directory in the top-file systemwhich points from the corresponding directory to the particular sub-filesystem containing the additional directory.
 9. The method of claim 8,wherein directories are stored at a root for the sub-file systems. 10.The method of claim 1, wherein: a symbolic pointer from the directory inthe top file system points to the sub-file system; each sub-file systemin the hierarchical file system is configured to recover from a failureindependently without an impact of a failure to other sub-file systems;and parallelizing file system operations by issuing the file systemoperations on any number of sub-file systems simultaneously.
 11. Themethod of claim 1, further comprising: receiving a request for a file inthe hierarchical file system; passing the request to a sub-file systemcontaining a directory containing the file; tracking the sub-filesystems to determine a rate that each sub-file system requestsadditional inodes; and upon the rate exceeding a threshold, increasinglyissuing more inodes for each inode request.
 12. A computer programproduct for storage management in a hierarchical file system, thecomputer program product comprising a computer readable storage mediumhaving program instructions embodied therewith, the program instructionsexecutable by a processor to cause the processor to: create, by theprocessor, a structure for the hierarchical file system including atop-file system and sub-file systems that each include files anddirectories; track, by the processor, directories for the sub-filesystems of the hierarchical file system; receive, by the processor, arequest for creation of a unique directory in the hierarchical filesystem; create, by the processor, based on applying a directory creationpolicy, a sub-file system of the hierarchical file system containing theunique directory while providing that each directory for the sub-filesystem resides in only one sub-file system; and upon a request by aparticular sub-file system for more inodes without any inodes available,revoke, by the processor, inode numbers from at least one other sub-filesystem having unused inodes; wherein failure in one sub-file system hasno affect on other sub-file systems in the hierarchical file system, andeach directory in the sub-file systems is named using an inode number ofa directory in the top file system.
 13. The computer program product ofclaim 12, further comprising program instructions executable by theprocessor to cause the processor to: maintain, by the processor, acorresponding directory in the top-file system; maintain, by theprocessor, a symbolic pointer in the corresponding directory whichpoints from the corresponding directory to the sub-file system where thetracked directory resides; and parallelize, by the processor, filesystem operations by issuing the file system operations on any number ofsub-file systems simultaneously.
 14. The computer program product ofclaim 12, wherein applying the directory creation policy comprises:determining that a particular sub-file system has available space for anadditional directory.
 15. The computer program product of claim 14,wherein determining comprises program instructions executable by theprocessor to cause the processor to: compare, by the processor,available space for each sub-file system; and select, by the processor,a sub-file system with the largest available space.
 16. The computerprogram product of claim 14, wherein determining comprises programinstructions executable by the processor to cause the processor to:select, by the processor, in a round-robin fashion, a sub-file systemhaving available space for the additional directory.
 17. The computerprogram product of claim 14, further comprising program instructionsexecutable by the processor to cause the processor to: create, by theprocessor, a corresponding directory in the top-file system; and create,by the processor, a symbolic pointer in the corresponding directory inthe top-file system which points from the corresponding directory to theparticular sub-file system containing the additional directory; wherein:a symbolic pointer from the directory in the top file system points tothe sub-file system; and each sub-file system in the hierarchical filesystem is configured to recover from a failure independently without animpact of a failure to other sub-file systems.
 18. An apparatuscomprising: a memory storing instructions; and one or more processorsexecuting the instructions to: create a structure for the hierarchicalfile system including a top-file system and sub-file systems that eachinclude files and directories; track directories for the sub-filesystems of the hierarchical file system; receive a request for creationof a unique directory in the hierarchical file system; create, based onapplying a directory creation policy, a sub-file system of thehierarchical file system containing the unique directory while providingthat each directory for the sub-file system resides in only one sub-filesystem; and upon a request by a particular sub-file system for moreinodes without any inodes available, revoke inode numbers from at leastone other sub-file system having unused inodes; wherein failure in onesub-file system has no affect on other sub-file systems in thehierarchical file system, and each directory in the sub-file systems isnamed using an inode number of a directory in the top file system. 19.The apparatus of claim 18, wherein the one or more processors furtherexecute instructions to: maintain a corresponding directory in thetop-file system; maintain a symbolic pointer in the correspondingdirectory which points from the corresponding directory to the sub-filesystem where the tracked directory resides; and parallelize file systemoperations by issuing the file system operations on any number ofsub-file systems simultaneously.
 20. The apparatus of claim 19, whereinthe one or more processors further execute instructions to: compareavailable space for each sub-file system; and select a sub-file systemwith the largest available space; wherein: a symbolic pointer from thedirectory in the top file system points to the sub-file system; and eachsub-file system in the hierarchical file system is configured to recoverfrom a failure independently without an impact of a failure to othersub-file systems.